This invention relates to electrical switches.
The background to the invention will be explained with reference to a particular application. Other applications will readily occur to the reader.
Motor vehicles are increasingly being fitted with air bags which expand, in the event of a collision, to protect the driver or passenger from impact with hard parts of the structure. In normal use, the bag would inflate and the occupant of the vehicle would then be thrown onto it. If, however, the bag were obstructed during inflation, the inflation pressure would be applied to the obstruction. The pressure although not great is sufficiently high to injure a person if s/he were to obstruct the inflating bag. In order to deploy the air bag in sufficient time to be of use, it must be expanded extremely quickly, so a person does not have the opportunity to get out of the way of an accidental inflation. This is of concern to motor mechanics, for example, who may have to work in the space into which the bag would inflate. It is desired, therefore to be able to deactivate the bag inflating mechanism. Another circumstance in which it would be desirable to deactivate the inflating mechanism, is when a rear-facing child's seat is carried on the front passenger seat of a motor car. It is desired that a switch for such purposes should be both inexpensive and highly reliable so that a mechanic, for example, can be sure the inflation mechanism is deactivated when working on the vehicle and so that the driver or passenger can be sure that the mechanism is properly reactivated. Conventional rotary switches either use a barrel cam arrangement to operate the contacts, or a moving contact wipes one or more fixed contacts, which would require contacts to be thickly gold plated or solid, for example, for reliability. Both arrangements would be undesirably expensive.
Against this background, there is provided an electrical rotary switch, having a rotary operating member mounted for rotation about an axis, at least one first contact member mounted for movement in opposed directions along a path transverse to but not intersecting the axis, between a first position in which a contact surface of the first contact member is in electrical contact with a contact surface of a respective second contact member and a second position in which the contact surfaces are not in electrical contact, the path being approximately normal to the contact surfaces, and the operating member having a surface to impart movement to the first contact member in one or both directions.
Since the path of movement is approximately normal to the contact surfaces, excessive wiping is avoided and reliability can be achieved with an inexpensive gold flashing, for example.
Reliability can be increased in a preferred embodiment, wherein said first contact member is resiliently flexible and wherein in said first position the operating member surface flexes the first contact member so as to apply pressure between the first and second contact members. The arrangement may provide significant pressure between the contact surfaces and a small degree of wiping in order to keep them clean. In this arrangement, index means is preferably provided to restrain the operating member in said first position and said second position. The index means counters the pressure of the first contact member.
In one convenient arrangement, the first contact member extends approximately parallel to but displaced from the axis.
In distinction from a conventional cam operated switch in which the cam extends generally in a plane transverse to the axis, said operating member surface preferably extends in a plane approximately parallel to the axis.
In one proposal, the operating member comprises: a body portion having an axial pin projecting from one side of said body, said pin being received by a hole in a stator so as to mount the body for rotary movement about the pin; and an arm spaced from said pin and extending in a longitudinal direction from said one side of the body, the arm providing said surface.
In that proposed arrangement, the arm is preferably generally L-shaped in section, having one portion extending in a direction approximately parallel to the axis, and another portion extending in a direction transverse to the axis and spaced from the body, said surface being provided on said other portion.
In order to reduce the possibility of the air bag mechanism being deactivated while the vehicle is being driven, the operating member is preferably movable by means of a removable key. In that case, the key can preferably only be removed in one of said first and second positions.